BCM2835 installed but giving undefined references

Question

So I installed BCM2835 but when I'm trying to compile a .c file with "gcc -c main main.c" it gives the following errors. I have no idea on how to compile linux btw, just follow stuff on the internet.

/tmp/ccSVwHkt.o: In function `main':
main.c:(.text+0x14): undefined reference to `bcm2835_init'
main.c:(.text+0x3c): undefined reference to `bcm2835_gpio_fsel'
main.c:(.text+0x48): undefined reference to `bcm2835_gpio_write'
main.c:(.text+0x50): undefined reference to `bcm2835_delay'
main.c:(.text+0x5c): undefined reference to `bcm2835_gpio_write'
main.c:(.text+0x64): undefined reference to `bcm2835_delay'
collect2: ld returned 1 exit status

This is the content of main.c (copied from Google code)

/*
 * main.c
 *
 *  Created on: 23-jun.-2013
 *      Author: Andreas Backx
 */


#include <bcm2835.h>
// Blinks on RPi Plug P1 pin 11 (which is GPIO pin 17)
#define PIN RPI_GPIO_P1_11
int main(int argc, char **argv)
{
    // If you call this, it will not actually access the GPIO
    // Use for testing
//    bcm2835_set_debug(1);
    if (!bcm2835_init())
        return 1;
    // Set the pin to be an output
    bcm2835_gpio_fsel(PIN, BCM2835_GPIO_FSEL_OUTP);
    // Blink
    while (1)
    {
        // Turn it on
        bcm2835_gpio_write(PIN, HIGH);

        // wait a bit
        bcm2835_delay(500);

        // turn it off
        bcm2835_gpio_write(PIN, LOW);

        // wait a bit
        bcm2835_delay(500);
    }
    bcm2835_close();
    return 0;
}

Answer 1

gcc -c main main.c doesn't make sense given the output you're getting. That said, if it's really what you're doing, you need to change it:

gcc -o main main.c

You'll likely still get the "undefined symbol" errors from the linker, since you're not linking with whatever library defines those symbols. A quick check of the examples at the site you linked shows that you need to link with the bcm2835 library:

gcc -o main main.c -lbcm2835

You may also need to add a -L flag if you installed the library somewhere where gcc doesn't know to look for it.